1. Technical Field
The present invention relates to an ultrasonic transducer for converting a voltage signal into an ultrasonic wave, an ultrasonic sensor, a method of manufacturing an ultrasonic transducer, and a method of manufacturing an ultrasonic sensor.
2. Related Art
In the past, there has been known micro electromechanical systems (MEMS) provided with ultrasonic transducers for outputting ultrasonic waves. Since the ultrasonic transducers provided to such MEMS are formed to have extremely small sizes, and therefore have thin film piezoelectric members used as sources of ultrasonic waves, and are typically configured to output the ultrasonic waves by displacing diaphragms using vibration of the thin film piezoelectric members (see, e.g., JP-A-2006-319945 (Document 1)).
The diaphragm-type ultrasonic sensor element described in Document 1 is provided with a diaphragm having a multilayer structure, and a PZT ceramic thin film layer provided to one side of the diaphragm and held between upper and lower electrodes. In such a diaphragm type ultrasonic sensor element, when applying a predetermined voltage to the PZT ceramic thin film layer through the upper and lower electrodes, the PZT ceramic thin film layer is elongated or contracted in an in-plane direction, and the diaphragm is distorted in a direction perpendicular to a surface direction in conjunction therewith to cause vibration, thereby outputting the ultrasonic wave.
Incidentally, in the element of Document 1 described above the amplitude of the vibration of the diaphragm corresponds to the amount of expansion or contraction of the PZT ceramic thin film layer in the in-plane direction, and is therefore not a large amount of displacement. Therefore, there arises a problem that the sound pressure of the ultrasonic wave is low.